For the delivery of radiation to treat cancer and a few nonmalignant diseases, radiotherapy requires precision in order to deliver more radiation to tumors and avoid excess radiation to normal tissues. Radiotherapy requires prior treatment planning, which involves corresponding diagnostic radiology scans, including, but not limited to, CT, MRI, MRS, PET/PET-CT scan and other nuclear medicine scans including, among others, SPECT and bone scans for precise positioning of the patient. After the planning scan, patients are typically treated with radiotherapy, with every effort to maintain the patient in the original planning position, anywhere from 1 to more than 45 times—often on a once-a-week, daily or twice-daily basis. Recent advancements in increased precision in radiotherapy delivery place great importance on the premise that the patients stay in the same position as during their planning scan(s).
There are 6 or more degrees of freedom in the position of a given part of the body on a day to day and intraday basis while a patient is on a treatment table or diagnostic table (FIG. 1). This includes translational motion in the x, y and z axis, as well as rotational shifts defined as pitch, roll or yaw. The spine is flexible and consists of multiple vertebral bodies; each vertebral body would have 6 degrees of freedom. This would be multiplied by the number of vertebral bodies would be at the same level as the treatment field (e.g., for head and neck radiotherapy, this would commonly extend from the skull, and the C1-T2 vertebral bodies=60 or more degrees of freedom).
Currently, there is no easy way of ensuring that a patient is positioned identically with their original planning scan. If a patient is undergoing or is to undergo radiation therapy, they can be immobilized according to the site of interest. In radiotherapy, in the example of head and neck cancer, this usually entails a custom-made mask for the head and an arch support for the neck. Both head and neck are immobilized onto the treatment table or diagnostic scan table. Tumors of the thorax, abdomen and pelvis may be positioned for treatment by immobilizing the legs and arms, but may require the creation of a rigid and patient-specific mold of the person's anatomy. The patient-specific mold would then be used with every treatment and every planning scan. Following immobilization, a patient is typically positioned with the placement of small pinpoint tattoos or other surrogate reference points on their body. The reference points are then lined up to a reference coordinate system, usually defined by a set of lasers and/or cameras. A set of 2-dimensional radiographs is taken, often on a daily, twice-weekly or weekly basis, in order to verify that a patient is aligned correctly in relation to bony anatomy and soft tissue silhouette.
Radiology or nuclear medicine scans including computed tomography (CT), magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), positron emission tomography (PET/PET-CT), Single Photon Emission Computed Tomography (SPECT), bone scan and other diagnostic scans including angiography are utilized in the diagnosis or in determining the extent of disease. Once disease is established, these or subsequent scans can be utilized to determine the targeting of localized therapies including radiation (radiation treatment planning) or other treatment modalities. If a patient undergoes several scans for purely diagnostic or assessment purposes (not for treatment planning), the position of the area of interest (e.g., an area of tumor that was previously excised with surgery or treated with radiation therapy, or a vascular malformation) is often determined on a patient only with respect to anatomical landmarks instead of with a coordinate system.
With the advent of sophisticated modes of radiation delivery, 2-dimensional radiography as discussed can be inadequate because sophisticated and ultra-precise delivery methods necessitate alignment in 3-dimensional space. This would require that a patient be scanned with either an in-room CT scanner or with a cone-beam CT scanner attached to the treatment linear accelerator, in order to verify the patient's position. However, the process of positioning a patient based on these radiological images is cumbersome, since it requires that many different points of a patient's anatomy be visually compared with that seen in the planning scan. Even if the matching process is automated, visual verification is difficult, especially since different parts of the body (e.g., parts of the spine) may vary in position semi-independently of each other. If a large mismatch is found, then the radiotherapy technician (RTT) or treating physician may prescribe a shift in the radiation or may need to reposition the patient. In such circumstances, obtaining greatest accuracy may entail another time-intensive rescan to verify the patient's position. For diagnostic radiology scans, a patient may be immobilized in the same manner and with the same tools as for radiotherapy (usually in the setting for radiotherapy planning purposes, or for radiology-guided procedures such as biopsy), or may be scanned in the most comfortable or neutral position for the patient on the scanning table with or without immobilizing devices.
Others have attempted to address problems outlined above. Primarily, these solutions have involved a method of imaging a patient more frequently, matching patient contours with a video camera system, or using infrared cameras to track fiducial markers that are attached to the skin. U.S. Pat. No. 4,262,306, U.S. Pat. No. 5,662,187, U.S. Pat. No. 5,727,554 and GB Patent 2,310,792, each of which is incorporated by reference herein in its entirety, teach imaging methods using camera devices to assess and monitor patient position during radiotherapy. U.S. Pat. No. 7,199,382, herein incorporated by reference in its entirety teaches x-ray imaging method to assess and monitor patient positioning. Systems for assessing respiration have used devices that track abdominal movement as a surrogate for respiratory motion, including a marker attached to the abdominal wall that is optically tracked or a belt that a patient wears around the abdomen or thorax containing a single pressure sensor to measure excursion with respiration as taught by U.S. Pat. No. 6,621,881, herein incorporated by reference in its entirety. Currently, there is a continuing unmet need for real time, patient positioning system and position monitoring system that minimizes or eliminates the requirement of time consuming radiology scans in radiotherapy and/or ensures patient positioning during radio-diagnostic procedures by sensing and/or detecting a patient's position during the course of the procedure to allow for current adjustments in patient position in radiation delivery.